Heat pumps are widely used for heating and cooling buildings primarily in moderate climates. Such heat pumps generally include a refrigeration system having a condenser exposed to ambient conditions and an evaporator exposed to the enclosure, house or other zone to be air conditioned so as to provide cooling for the zone. To heat the zone, suitable means, generally including flow control valves, are provided to transfer heat required for the evaporation portion of the process to the ambient surroundings, and to transfer heat generated by the condenser portion of the process to the zone. The reason such systems are primarily used in moderate climates is because of the relatively limited heat output capability for the refrigeration system's condenser.
This invention relates to a working fluid and, to a process specifically designed to include a heat pump system to provide, optionally, heat and/or refrigeration by suitable heat exchange, using operations that include vaporization, expansion, and condensation of a chemically and thermally stable refrigerant which is alternately absorbed and desorbed from the working fluid without using a compressor. More particularly, the invention relates to a heat pump based on an absorption system which uses an improved working fluid, and the heat pump may be used either continuously or in a cyclical (that is, "batch-type") operation, depending upon the work it is to perform. The working fluid is a liquid ammoniate formed by ammoniating ammonium chloride to form a reaction product or complex (hereafter "complex" for brevity) of ammonia with the ammonium chloride, and is not a simple physical solution of the chloride in ammonia, but chemically combined with it. To function as the absorbent, the working fluid is the complex containing no more ammonia than is effective to make the absorbent a pumpable liquid, in which state the absorbent is therefore referred to as a "low ammoniate". After the absorbent has reacted with and absorbed as much ammonia as it can, the working fluid becomes a highly ammoniated complex (hence referred to as "high ammoniate") which is to be desorbed in the generator.
As long ago as the begining of this century it was known that various thiocyantes and the nitrate, bromide and iodide of ammonia were well-adapted for use in an absorption system. The use of these salts in elemental refrigeration systems is disclosed in U.S. Pat. Nos. 925,039 and 1,042,041 to William W. Seay who used a single vessel which served both as absorber and generator. In the earlier system of the '039 patent he converted a solid salt to liquid ammoniate, and after desorbing the ammonia, the solid salt was re-formed. In the later '041 patent he recognized the advantage of maintaining the ammoniate in liquid form. But such systems appear to have been largely disregarded for a variety of technical and economical reasons. Seay missed the fact that ammonium chloride was particularly well-suited to his purpose. As is well-known to those skilled in the art, it is knowledge of the physical and chemical properties of a material which suggests its utility for a particular purpose.
Nearly a half century later, U.S. Pat. No. 2,986,525 to Hughes discloses the use of anhydrous mixtures of the halides of the alkaline earth metals and various nitrates and chlorides such as lithium and ammonium nitrates or chlorides to form a strong porous mass for absorption of ammonia when the mass is cooled, and desorption of the ammonia when the mass is heated. The salts, one of which may be ammonium chloride, are fused and intimately blended together to form a "eutectoid". Because the entire porous mass is to be alternately cooled when it is to function as an absorber, and then heated when it is to function as a generator in which ammonia is desorbed, operation of the '525 absorption refrigeration system is necessarily cyclical. The absorbent cannot be continuously circulated between the absorber and the generator. Since it is known that ammonium chloride is essentially insoluble in a complex of ammonium chloride and ammonia, there was no reason, particularly in view of the disclosed preference of a eutectoid, to expect that a complex formed by approximately equimolar quantities of ammonium chloride and ammonia would provide a pumpable liquid especially well-adapted for use as the absorbent in a continuously or cyclically operable heat pump in which the energy is provided by a heat source below 100.degree. C. This anomolous physical property of ammonium chloride, inter alia, which is quite distinct from the behavior of other ammonium salts, presumably accounts for its (the chloride's) exclusion from the many salts suggested by Seay, supra.
The well-known ammonia-water system, though popular, uses a solution of ammonia in water and requires high operating pressures generally ranging up to about 400 pounds per square inch (psi), a source of high temperature heat above 100.degree. C., and a rectifier to free the ammonia from entrained water. Also well-known is the lithium bromide-water combination and variations thereof, but such absorption-refrigeration systems are operated at subatmospheric pressures as disclosed in U.S. Pat. No. 3,541,013 to Macriss et al.
Less commonly used systems disclosed in the prior art use working fluids such as various organic fluid mixtures such as methylene chloride and substituted polyglycols described in U.S. Pat. No. 2,149,947 to Zellhofer. No prior art system which I know of uses ammoniated ammonium chloride as the working fluid in an absorption refrigeration system, or is so well-adapted for use with a geothermal heat source or a solar collector from which the available temperature is limited to about 80.degree. C.
U.S. Pat. No. 3,458,445 to Macriss et al recognizes the importance of the practical considerations which are so critical with respect to the selection of the elemental parts of an absorption refrigeration system and compares the operation of earlier systems with one which uses a solution of monomethylamine and sodium thiocyanate as the working fluid. Clearly delineated is the importance of the choice of the working fluid because it will determine the coefficient of performance for the system, the cost of the equipment in the system, including, for example, whether or not a rectifier may be essential. Most important, neither the '445 patent nor any other prior art reference disclosing ammonia as the refrigerant suggests the desirability of formulating a working fluid which would function in a generator which is operable under charging conditions with a source of low temperature heat at a temperature below 80.degree. C. In an environment of already high and steadily increasing energy costs, there is a great need to utilize heat from relatively low temperature heat sources which to date have defied profitable utilization. This invention provides a practical heating/refrigeration absorption system which can profitably utilize fluids heated with solar energy, geothermal fluids, and heat from process streams now wasted.